This invention relates generally to pressure switches and more particularly to pressure switches particularly adapted for use with high pressure fluid for actuating a switch mechanism in response to changes in fluid pressure being monitored.
There has been in recent years marked technical progress in the field of pneumatic and hydraulic systems which has led to the need for the development of a small sized, durable and high reliability pressure switch capable of withstanding high fluid pressure. In the field of braking systems and power steering systems for the automotive industry in recent years, for example, there has been a demand for the development of a pressure switch adapted for use with high pressure fluid, small in size, light in weight, with improved safety and highly reliable for an extended period of time for the purpose of achieving improved fuel efficiency.
Typical examples of pressure switches made according to the prior art include one in which a thin film type of flexible diaphragm is displaced in response to fluid pressure with the contact of a switching mechanism being actuated by the displacement of this diaphragm. Another example is one in which the peripheral edge of a diaphragm, in the form of a metallic disc, is fixed to a housing by such means as welding, the center of the diaphragm being moved between convex and concave configurations by the pressure differential between the two sides of the disc, with the contact of the switching mechanism being actuated in response to the disc movement.
The pressure switch of the latter type is such that the diaphragm serves both as a fluid seal and as a component part that carries out the actuating movement.
However, a problem is associated with the former pressure switch described above in that a high stress is generated locally in the diaphragm, thereby markedly reducing the life of the diaphragm. With respect to the latter type described above, welding of the peripheral portion of the diaphragm results in a possibility for the attachment operation to adversely affect the reliability of the switch. Further, extra effort and time are required in manufacturing, thereby creating a problem in terms of production.
There is an additional problem with either of the above switches in that their reliability can not be satisfactorily ensured when used with high fluid pressure, for example, in the range between 100 and 200 kilograms per square centimeter as is required in the case of the latest high pressure type pressure switches, even though they are capable of carrying out ordinary switching action when used with comparatively low fluid pressures, for example, in the range between 35 and 75 kilograms per square centimeter.
In the case of the pressure switches according to the prior art as described above when used with high pressure, it has been necessary in the past to increase the thickness of the components as well as the size of the member supporting the diaphragm in order to withstand the heavy loads that are added repeatedly when the fluid pressure becomes higher and the force applied to the diaphragm becomes extremely large.
Yet another example of prior art pressure switches employs a ring-shaped support placed under the diaphragm to limit the displaced portion of the diaphragm to the central part facing a central opening of the support. According to this construction, however, especially when used with high pressure fluids, a large localized stress is generated in the diaphragm at the edge of the central opening of the ring-shaped support when the diaphragm is displaced with a consequent result that the diaphragm tends to be adversely affected, thereby shortening the life of the diaphragm and consequently the life of the switch itself.
A pressure switch using a diaphragm or cap made of rubber has also been proposed. However, the rubber hardens in low temperature environments, becoming relatively rigid and thus seriously affecting the switching function. In addition, a diaphragm made of rubber tends to be easily worn out at the portions of engagement with the movable member of the switch mechanism. This presents a further problem in that, because of this wear, the interior of the switch mechanism can become contaminated thereby shortening the life of the switch.